s1 = "Thank you!"
s2 = "you"

def fun(s1, s2):
    l1 = list(s1)
    l2 = list(s2)
    for i in l2:
        if i in l1:
            l1.remove(i)

    s = ""
    for i in l1:
        s += i
    return s




# 方法2
def func(str, sub):
    s = set(sub)
    ans = ''
    for c in str:
        if c not in s:
            ans += c
    return ans


print(fun(s1, s2))
print(func(s1, s2))